Among current endeavors to explore renewable energy technologies, photoelectrochemical (PEC) water splitting holds great promise for the conversion of solar energy to chemical energy. Light absorption, charge separation, and appropriate interfacial redox reactions are three key aspects that lead to highly efficient solar energy conversion via PEC water splitting. Therefore, the development of high-performance PEC electrodes has concentrated largely on engineering the band structure of photoanodes, enlarging the semiconductor-electrolyte interfacial area, and enabling rapid charge separation, collection, and transportation. High porosity three dimensional (3D) nanostructures, such as branched nanowire architectures and nanofiber networks, offer extremely large surface area, excellent charge transport properties, and long optical paths for efficient light absorption. As a result, 3D nanostructures are of interest in PEC photoanode development.